1. Field of the Invention
The present invention relates to a holding seal material, an exhaust gas purifying apparatus, and a method of manufacturing a holding seal material.
2. Discussion of the Background
In exhaust gas exhausted from an internal combustion engine, such as a diesel engine, particulate matter (hereinafter also referred to as PM) is included, and, in recent years, the harmful influence of PM on the environment or human bodies has become a problem. In addition, since harmful gas components, such as CO, HC and NOx, are included in exhaust gas, there is a concern as well regarding the influence of the harmful gas components on the environment or human bodies.
Therefore, as an exhaust gas purifying apparatus that collects PM in exhaust gas or purifies the harmful gas components, a variety of exhaust gas purifying apparatuses configured of an exhaust gas treatment body made of a porous ceramic, such as silicon carbide or cordierite, a casing that accommodates the exhaust gas treatment body, and a holding seal material disposed between the exhaust gas treatment body and the casing are proposed. The holding seal material is disposed mainly for preventing the exhaust gas treatment body from coming into contact with the casing that covers the outer circumference of the exhaust gas treatment body and being broken, which may be caused by vibrations or impacts generated due to the traveling and the like of an automobile, or for preventing the leakage of exhaust gas between the exhaust gas treatment body and the casing.
Here, for internal combustion engines, there is a tendency to increase the temperature and pressure of exhaust gas in order to run internal combustion engines under conditions close to the theoretical air fuel ratio for the purpose of improving the gas mileage. When high-temperature and high-pressure exhaust gas reaches the exhaust gas purifying apparatus, since there are cases in which the gap between the exhaust gas treatment body and the casing varies due to the difference in thermal expansion coefficient between the exhaust gas treatment body and the casing, there is a demand for the holding seal material to have a holding force for the exhaust gas treatment body, which does not change due to a certain degree of variation of the gap.
In order to improve the holding performance of the holding seal material, JP-A-2002-206421 describes the attachment of inorganic particles to the surfaces of inorganic fibers.